a. Field of Invention
This invention relates to a plunging type tripod type constant velocity universal joint. Generally, a constant velocity universal joint is a kind of constant velocity universal joint joining two shafts, on the driving and driven sides, and capable of transmitting torque at constant velocity even if there is an angle between the two shafts, wherein the plunging type allows relative axial displacement between the two shafts, while the tripod type is such that a tripod member provided with three radially projecting trunnions is connected to one shaft and a hollow cylindrical outer joint member provided with three axially extending track grooves is connected to the other shaft, the trunnions of the tripod member being received in the track grooves of the outer joint member to effect transmission of torque.
b. Prior Art
An example of the plunging type tripod type constant velocity universal joint will be described with reference to FIG. 13A. It is constructed in such a manner that the inner peripheral surface of an outer joint member 1 is formed with three axial track grooves 2, and that annular rollers 7 rotatably fitted through a plurality of needle rollers 6 on the cylindrical outer peripheral surfaces of three radially projecting trunnions 5 of a tripod member 4 inserted in the outer joint member 1 are inserted in the track grooves 2. A pair of roller guide surfaces 3 opposed to each other circumferentially of each track groove 2 are concave surfaces (partial cylindrical surfaces) parallel with the axis of the outer joint member 1, while the outer peripheral surface of the roller 7 on each of the three trunnions 5 is a convex surface (partial spherical surface) fit to the roller guide surfaces 3. Each roller 7 is movable axially of the outer joint member 1 along the track groove 2 while engaging the roller guide surfaces 3 of the corresponding track groove 2 and rotating around the axis of the trunnion 5.
When the joint transmits torque at an operating angle xcex8 as shown in FIG. 13B, the relationship is such that the roller 7 and the roller guide surfaces 3 obliquely cross each other as shown in FIG. 13C. In this case, the roller 7 tends to rollingly travel in the direction of arrow t in FIG. 13B, whereas since the roller guide surfaces 3 are partial cylindrical surfaces parallel with the axis of the outer joint member 1, the roller 7 will move while being restrained by the roller guide surfaces 3. As a result, sliding friction occurs between the roller guide surfaces 3 and the roller 7 and sliding resistance is produced. Further, this sliding friction produces induced thrust in the axial direction. Such sliding resistance and induced thrust cause vibration and noise in the car body, influencing the noise, vibration, hardness or NVH performance of automobiles, lowering the flexibility of design of suspensions for vehicles.
As for such plunging type tripod type constant velocity universal joint intended to reduce sliding resistance and induced thrust, for example, one having a construction shown in FIG. 14A is known. As shown, the outer peripheral surfaces of the trunnions 5 of the tripod member 4 are true spherical surfaces, and the cylindrical inner peripheral surface of a cylindrical ring 8 is slidably fitted on the true spherical surface. The ring 8 and roller 7 constitute a roller assembly relatively rotatable through needle rollers 6. The needle rollers 6 are arranged in the full complement bearing condition between the cylindrical outer peripheral surface of the ring 8 and the cylindrical inner peripheral surface of the roller 7 and an annular washer 9 prevents the needle rollers 6 from slipping off. The roller 7 is received in the track groove 2 of the outer joint member 1 and is movable axially of the outer joint member 1 while rolling on the roller guide surfaces 3 of the track groove 2.
The outer peripheral surface of the trunnion 5 is a true spherical surface having a center of curvature on the axis of the trunnion 5, and the roller assembly (7, 8, 9) oscillates around the center of curvature. Since the roller assembly is capable of oscillation, when torque is transmitted at an operating angle formed between the outer joint member 1 and the tripod member 4, the roller 7 is guided by the roller guide surfaces 3 of the outer joint member 1 such that the roller 7 keeps its position parallel with the axis of the outer joint member 1, and with the position unchanged, it correctly rolls on the roller guide surfaces 3. Therefore, the sliding friction reduces when torque is transmitted at a operating angle, and the sliding resistance and the occurrence of induced thrust are suppressed.
It is known to use a plunging type tripod type constant velocity universal joint for transmitting torque from an automobile engine to wheels at constant velocity. A plunging type tripod type constant velocity universal joint, which has spherical rollers attached to the trunnions of a tripod member, is used as a full complement type in which needle rollers serving as rolling elements between the outer peripheral surfaces of the trunnions and the inner peripheral surfaces of the spherical rollers have no cage. And when torque is transmitted at an angle, friction between internal parts causes induced thrust during rotation and forceful axial extension and contraction even in the stopped state causes sliding resistance. As NVH phenomena typical of automobiles taking part in such induced thrust and sliding resistance, there is swaying of the car body occurring in connection with the former during traveling and in connection with the latter there is an idling vibration phenomenon in the drive or D range of an automatic transmission or AT car during stoppage.
Concerning NVH problems of automobiles, the key point for solution is to reduce the induced thrust and sliding resistance of the joint. Generally, the induced thrust and sliding resistance of the joint tend to depend on the size of the operating angle. Therefore, when the joint is to be applied to the drive shaft of an automobile, there occurs a problem of design limitation that a greater operating angle cannot be employed. Therefore, in order to increase the flexibility of design of suspensions for automobiles, it has been necessary to reduce and stabilize induced thrust and sliding resistance.
However, in the conventional plunging type tripod type constant velocity universal joint, since the rolling elements are needle rollers of the full complement type, eccentric loads, such as edge load, tend to act on the rolling element surfaces due to the skewing of the rollers during rotation, etc. Further, the state of contact does not stabilize due to internal clearances and accuracy, and edge load occurs even when the spherical rollers are inclined. Further, structurally, relative slide also occurs between the end of the spherical roller, the trunnion and the washer. Such phenomena as skewing, edge load and relative slide are thought to govern the magnitude of the frictional force in the joint interior.
Accordingly, an object of the invention is to minimize these frictional forces to further reduce and stabilize induced thrust and sliding resistance.
The invention provides a constant velocity universal joint comprising an outer joint member formed with three track grooves having roller guide surfaces arranged in circumferentially opposed relation to each other, a tripod member having three radially projecting trunnions, rollers inserted in the track grooves, and rings fitted on the trunnions to support the rollers for rotation, the rollers being movable along the roller guide surfaces axially of the outer joint member, wherein the roller is composed of a set of annular roller portions and a plurality of balls are interposed between outer raceway surfaces formed in rows each in the inner periphery of the annular roller portion and two rows of inner raceway surfaces formed in the outer periphery of the ring.
The roller composed of a set of roller portions includes not only two-split roller but also three- or more-part rollers, and a roller in which an intermediate body is interposed between adjacent roller portions. Therefore, in the case of a two-split roller, each roller portion has an outer raceway surface. In the case of a three-part roller, for example, roller portions on opposite sides will be provided each with a outer raceway surface.
Since the roller is of split construction, composed of a set of roller portions, relative rotation of the roller portions is allowed, reducing the sliding resistance and rolling resistance. That is, when torque is transmitted with an operating angle defined between the outer joint member and the tripod member, some rollers swing while describing an arc with respect to the roller guide surface. Since the positions of contact between individual roller portions and the roller guide surface are spaced axially of the trunnion, the distances from the positions of contact between the individual roller portions and the roller guide surface to the axis of the tripod member differ and the peripheral speeds of the two roller portions differ from each other. As the result of the peripheral speeds differing from each other, an angular positional deviation of the roller portions would otherwise occur; however, since relative rotation of the roller portions is possible, such angular positional deviation is accommodated by the relative rotation of the roller portions. Therefore, the sliding resistance and rolling resistance encountered when the roller swings in an arc on the roller guide surfaces are reduced. Further, the split construction of the roller facilitates incorporation of balls and saves the need for providing a receiving groove.
Since the roller interposed between the tripod member and the outer joint member is supported by balls making smooth low-friction rotation at all times without such problems as skewing, a low-friction low-resistance rolling movement is realized when the roller rolls in the track groove of the outer joint member along the roller guide surfaces. Therefore, the sliding resistance produced when the roller slides in the track groove axially of the outer joint member and hence the induced thrust produced when torque is transmitted with an operating angle defined between the outer joint member and the tripod member are further reduced; thus, a high performance, plunging type tripod type constant velocity universal joint producing little vibration or noise can be provided.
Further, supporting the roller by a double row of balls increases the load capacity against moment loads and increases durability, as compared with supporting it by a single row of balls. The spacing between the ball rows can be optionally set. With the ball diameter taken as a criterion, for example, the spacing may be greater or smaller than the ball diameter. In the latter case, the balls in one row will circumferentially alternate with the balls in the other row, e.g., one by one, so that the required number of balls is reduced as a whole, contributing to weight reduction. Further, reducing the spacing between the ball rows reduces the axial spacing from the position of contact between the balls and the roller, and it is thought that it becomes easier for the roller portions to make synchronous rotation.
The inner peripheral surface of the ring may have a convexly arcuate section and the outer peripheral surface of the trunnion a sectional shape which contacts the inner peripheral surface of the ring in a direction orthogonal to the axis of the joint and which defines a clearance between itself and the inner peripheral surface of the ring axially of the joint.
Concerning the cross sectional shape of the trunnion, a shape which contacts the inner peripheral surface of the ring in a direction orthogonal to the axis of the joint and which defines a clearance between itself and the inner peripheral surface of the ring axially of the joint, means, in other words, a shape such that the surfaces opposed to each other axially of the tripod member are retracted toward each other, i.e., toward the smaller diameter side from an imaginary cylindrical surface. A concrete example thereof is an elliptic shape. The term xe2x80x9celliptic shapexe2x80x9d as used herein is not limited to literally ellipse but shall include those shapes which are referred to generally as oval shapes.
By employing the shape as the cross sectional shape of the trunnion, the trunnion is allowed to incline with respect to the outer joint member without changing the attitude of the roller assembly when the joint takes an operating angle. Furthermore, as is clear by comparing FIGS. 3 and 14C, since the contact ellipse between the outer peripheral surface of the trunnion and the ring approaches a dot from an oblong, the friction moment tending to incline the roller assembly is reduced. Therefore, the attitude of the roller assembly is stable at all times and the roller is held parallel with the roller guide surfaces, so that it can roll smoothly. This contributes to the reduction of sliding resistance and hence the reduction of induced thrust. Further, there is another advantage that the bending strength of the trunnion is improved due to the increase of the modulus of section of the root of the trunnion. In addition, it is not necessary for the inner peripheral surface of the ring to be of cylindrical shape extending throughout the length; the central portion alone which contacts the trunnion may be cylindrical and the opposite ends may be formed with a relief portion for avoiding interference when the trunnion is inclined.
The roller assembly is interposed between the trunnion and the outer joint member and performs the role of transmitting torque. Since the direction of transmission of torque in this kind of constant velocity universal joint is always orthogonal to the axis of the joint, torque transmission is possible in that the trunnion and the ring are in contact with each other in the direction of torque transmission; even if there is a clearance between the two axially of the joint, there is no hindrance to torque transmission.
Furthermore, since the trunnion can be inclined without inclining the ring, it is possible for the roller to roll smoothly on the roller guide surfaces without being inclined. Therefore, a flange which is sometimes provided in the track groove of the outer joint member for the purpose of controlling the inclination of the roller can be omitted. Omission of such flange achieves not only weight reduction of the outer joint member and simplification of processing but also eliminates the sliding resistance which is caused by sliding contact between the roller and the flange, with the result that further reduction of the sliding resistance and reduction of the induced thrust can be achieved.
The invention is not limited to a form in which the cross section of the trunnion is substantially elliptic, as described above, and is applicable, e.g., to the following arrangements. That is, the inner peripheral surface of the ring may be cylindrical and the outer peripheral surface of the trunnion spherical. A cylindrical bush whose outer peripheral surface is convexly spherical and whose inner peripheral surface is cylindrical may be interposed between the concavely spherical inner peripheral surface of the ring and the cylindrical outer peripheral surface of the trunnion. The longitudinal section of the outer peripheral surface of the roller may be convexly arcuate and the cross section of the roller guide surface concavely arcuate.
The ball and the raceway surface may contact each other at a contact angle. This increases rigidity, thus serving to improve load capacity and durability.
The roller and the roller guide surface may make angular contact with each other. The fact that the roller and the roller guide surfaces make angular contact with each other ensures that the roller hardly deviates and has its attitude further stabilized so that when moving axially of the outer joint member, the roller rolls on the roller guide surfaces smoothly with less resistance. As a concrete example of an arrangement for realizing such angular contact, there may be cited an arrangement in which the generating line of the outer peripheral surface of the roller is a convex arc while the sectional shape of the roller guide surface is a taper or Gothic arch.
The invention thus provides a constant velocity universal joint comprising an outer joint member formed with three track grooves having roller guide surfaces arranged in circumferentially opposed relation to each other, a tripod member having three radially projecting trunnions, rollers inserted in the track grooves, and rings fitted on the trunnions to support the rollers for rotation, the roller being movable along the roller guide surfaces axially of the outer joint member, wherein the roller is composed of a set of annular roller portions and a plurality of balls are interposed between outer raceway surfaces formed in rows each in the inner periphery of the annular roller portion and two rows of inner raceway surfaces formed in the outer periphery of the ring; as a result, the rollers are supported by the balls constantly making smooth low-friction rotation without any problem, such as skewing, and low-friction low-resistance rolling is realized when the rollers are rolling in the track grooves of the outer joint member along the roller guide surfaces. Therefore, a high performance plunging type tripod type constant velocity universal joint can be provided in which the sliding resistance which occurs when the rollers slide in the track grooves axially of the outer joint member, and hence the induced thrust which occurs when torque is transmitted with an operating angle defined between the outer joint member and the tripod member, are further reduced and there is little vibration or noise.
A ring whose inner peripheral surface has a convexly arcuate section is fitted on the outer peripheral surface of a trunnion contacting the inner peripheral surface of the ring in a direction orthogonal to the axis of the joint and having a sectional shape which defines a clearance between itself and the inner peripheral surface of the ring axially of the joint; this arrangement allows the trunnion to incline with respect to the outer joint member without changing the attitude of the roller assembly when the joint takes an operating angle. Furthermore, since the contact ellipse between the outer peripheral surface of the trunnion and the ring approaches a dot from an oblong, the friction moment tending to incline the roller assembly is reduced. Therefore, the attitude of the roller assembly is stable at all times and the roller is held parallel with the roller guide surfaces, so that it can roll smoothly. This contributes to the reduction of sliding resistance and hence the reduction of induced thrust. Further, there is another advantage that the bending strength of the trunnion is improved due to the increase of the modulus of section of the root of the trunnion.
If applied particularly to the drive shaft of an automobile, the constant velocity universal joint of the invention can contribute to the improvement of the NVH characteristics of the automobile which the magnitudes of sliding resistance and induced thrust take part in, and the flexibility of design of suspensions for automobiles is also increased.